This invention relates to a conveyor system for providing head-to-head and/or head-to-tail placement of product. More specifically, my system is configured to use the minimum acceleration necessary to perform the placement of product in relation to each other. Feedback control continuously readjusts acceleration to perform the given work.
Industry long has faced a problem of increased conveyor wear and tear at ever increasingly higher conveyor speeds in order to handle throughput requirements. Another problem is that it becomes increasingly more difficult accurately control items as conveyor speeds increase. One way to minimize the requirement of increasing conveyor speed is by keeping the air gap produced between items to the minimum that is required. This also has the added effect of providing higher throughput rates than could otherwise be achieved without changing the overall speed of the conveyor (if retrofitting an existing conveyor system for instance).
In targeting a gap industry has faced the problem of being able to open/close gap by any significant amount and handle the item in gentle fashion. Invention overcomes this problem and can provide gentler product handling than other prior art methods by its ability to split the work of opening/closing gap in a desired fashion over multiple conveyor sections working together. This approach can reduce the amount of expensive drives, electrical controls, and maintenance that may be required as compared with some other prior art methods reducing overall system cost. In targeting placement of product in relation to another, invention can be used with in-line scales, etc. by its ability to establish a head-to-head gap as well.
Prior art has taken various approaches to the above issues. One approach was simply to count on a speed ratio to ensure there is sufficient gap between items. Another approach was to use variable speed motor controllers or constant speed controllers to control the conveyors. A recent system uses a speed control on the upstream conveyor with three settings. The settings were nominal, higher than nominal and lower than nominal. Obviously, this method does not account for feeding a conveyor that has no nominal speed (one that can accelerate and decelerate) or to feed product at something other than the nominal speed (i.e. product may target a speed higher or lower than downstream conveyor is traveling). Additionally, flexibility is lost when the speed control limits are defined by the conveyor instead of the product that is on the conveyor. Unlike other prior art, my system targets the placement of product in relation to another as opposed to just spacing of product. Placement of product provides the added ability to target head-to-head gap as well as a head-to-tail gap.
My system uses one or more contiguous variable speed conveyors that work together to space items at a predefined gap at each output juncture using minimum acceleration necessary to perform the given work. Feedback control is used to continually readjust acceleration as necessary to meet spacing requirements.
The system is a conveyor system for providing targeted head-to-tail spacing and/or head-to-head spacing between product including a product of influence comprising:
a first device having a conveyor, a device entry point and a device exit point;
a free space having an end point downstream of the exit point of the first device;
a monitor for monitoring movement of the product of influence in the first device;
a computer responsive to the movement of the product of influence in the first device programmed to determine a start-of-synch point and an end-of-synch point;
a speed control responsive to the computer for controlling the velocity and/or acceleration of the conveyor of first/subsequent devices;
wherein the computer also is programmed to determine the acceleration needed for the product of influence to travel from the start-of-synch point to the end point of the free space;
wherein the computer also is programmed to set a synch velocity which is the velocity of the first device when the front of synch point reaches the first device exit point plus free space; and
wherein the speed control responsive to the computer continues the synch velocity until the end-of-synch point reaches the first device exit point.
A downstream conveyor can be variable in speed as long as the behavior of downstream conveyor can be anticipated. As item progresses across the first device at time interval x (where x is a constant), the minimum accel/decel is recalculated based on actual movement of the conveyor and estimated movement during each time interval x. This is the feedback control that increases or decreases acceleration of conveyor based on actual movement y and estimated movement during time interval x. Y is actual measured movement of the first device. Note that estimated movement is never incremented beyond the resolution of y. If y is 1 inch then estimated movement increments to 1 inchxe2x80x94but not beyond. The converse is also true, if actual movement y (1 inch in this example) is detected and estimated movement is 0.5 inches, actual movement is changed from 0.5 inches to 1 inch (y always takes precedence over estimated movement during time x).
The first device uses this information to calculate the acceleration required (every time interval x). It also calculates what its velocity and distance traveled should be at the next interval x. Minimum acceleration is being recalculated every time interval x. If the first device falls behind or gets ahead the calculated acceleration will increase or decrease. This is the feedback control.
Feedback control allows for more accurate product positioning than could otherwise be achieved. It also has the ability to use non-precise equipment and obtain acceptable results. An example of using non-precise equipment to obtain acceptable results is a VFD with limited number of accel/decel digital input commands. In this case the accel/decel command to the VFD that best fits the desired (calculated minimum) accel/decel.